LCD suppliers bettering performance of color screens

As demand for high-content color displays in PDAs and mobile handsets grows, LCD makers continue to add new products to improve viewability while reducing size and simplifying integration.

iSuppli/Stanford Resources projects that the market for color LCDs in PDAs and cell phones will grow from a respective 14 million and 533 million units this year to 24 million and 770 million units in 2006. By next year, there will be color LCDs in 50% of all cell phones and PDAs, according to the El Segundo, Calif., research firm.

The need for higher resolution and color contrast is driving the development in particular of active-matrix LCDs that use amorphous silicon, continuous grain silicon, or low-temperature polysilicon technologies.

Royal Philips Electronics last month announced that it will begin producing next quarter low-temperature polysilicon LCD modules that can embed a number of circuit functions, including the DC/DC converter and capacitors, directly onto the display's glass.

This arrangement enables the display to require just single-supply voltage, making it easier to integrate into mobile phones, according to the company, which is headquartered in the Netherlands.

"This idea is becoming a bit more mainstream," said Peter Hopper, chief executive of Philips' Mobile Displays Group. "It's a trend we consider important for the mid- to long term."

Philips' display provides a contrast ratio of 100:1 in transmission mode and brightness of 150 candelas per square meter. Resolution is 176 ¥ 220 pixels. Hopper said the display will be customized to user requirements for high-end mobile phones.

Philips will still offer both amorphous silicon and twisted-nematic LCDs for applications with less stringent requirements, he added. "We believe that for the next few years, a num-ber of color LCD technologies will co-exist."

Philips is not the first to integrate components onto LCD glass. Sharp Electronics Corp. of Japan, for instance, has offered over the past year continuous-grain silicon displays with integrated drivers on the glass. Sharp has two plants producing such displays, with a combined capacity of 6.5 million 2in. units a month.

The company's patented continuous-grain silicon technology uses fewer layers than low-temperature polysilicon, while promising higher performance at competitive cost, according to Joel Pollack, vice president of the displays business unit for Sharp's U.S. subsidiary, Sharp Microelectronics of the Americas Inc., Camas, Wash.

"We found that low-temperature polysilicon restricts the resolution to under VGA [640 ¥ 480 pixels]," Pollack said, adding that Sharp's displays are capable of VGA-quality resolution.

But like Philips, Sharp is continuing to offer active-matrix LCDs that use amorphous silicon to meet various user requirements. Last month, the company introduced a 3.5in. transflective TFT-LCD with a brightness of 100 candelas per square meter, providing optimal viewability in either bright sunlight or dark lighting.

Sharp's LQ035Q7DH01 has a 100:1 contrast ratio, consumes less than 365mW, and exhibits a 30ms response time. The display costs $145 in quantities of 50.

Samsung Electronics Co. Ltd., Seoul, Korea, has migrated amorphous-silicon technology from its larger TFT-LCDs to mobile phone displays, producing a 2.2in. LCD with a resolution of up to 320 ¥ 240 pixels, or about 180 pixels per inch.

The company also announced a 1.8in. active-matrix TFT-LCD using amorphous silicon, driven by a single IC and backlight. This design allows the LCD to be made 1mm thinner than other 1.8in. panels, reducing the bill of materials.

Samsung plans to convert several older LCD fabs in Gilheung, Korea, to meet increasing market demand for small LCDs. The company said it is now selling more than 2 million small LCDs a month.